POSTGANGLIONIC SYMPATHETIC  NERVE ENDING
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POSTGANGLIONIC SYMPATHETIC NERVE ENDING. Na. Norepinephrine (NE). Tyrosine. Dopa. Tyrosine. SYNTHESIS. DA. STORAGE. NE. RELEASE. Ca. ACTION. REUPTAKE. NET. DEGRADE. Dopamine (DA). NE  E. E. ADRENAL MEDULLA. COMT. PHARMACOLOGY OF SNS. According to chemistry.

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POSTGANGLIONIC SYMPATHETIC NERVE ENDING

Na

Norepinephrine (NE)

Tyrosine

Dopa

Tyrosine

SYNTHESIS

DA

STORAGE

NE

RELEASE

Ca

ACTION

REUPTAKE

NET

DEGRADE

Dopamine (DA)

NE  E

E

ADRENAL MEDULLA

COMT


PHARMACOLOGY OF SNS


According to chemistry

According to spectrum of action

According to mode of action

Adrenoceptor Blockers

Adrenolytics

Adrenergic Neuron Blockers Sympatholytics

Alpha & beta- adrenergic receptor blockers


ADRENERGICS STIMULANTS [AGONISTS]

Direct Sympathomimetics

Indirect Sympathomimetics

Dual Sympathomimetics


ADRENERGIC STIMULANTS

According to chemistry; Catecholamines; Natural; NE, E, Dopamine

Synthetic; Isoprenaline

Rapidly acting / Degraded by MOA & COMT

Sparse CNS effects / Parenterally administered

Non-Catecholamines; Ephedrine

Delayed action / Resist degradation by MOA

Prominant CNS effects / Orally administered

According to spectrum of action;

Non-Selective;

Norepinephrine, epinephrine, dopamine, isoprenaline, ephedrine,…etc

Selective;

a1; Phenylephrine

a2; Clonidine

b1; Dobutamine

b2; Salbutamol


ADRENERGIC STIMULANTS

According to mode of action;

Direct; Stimulate adrenergic receptors directly.

e.g. adrenaline, noraderanaline, dopamine, isoprenaline, phenylephrine, methoxamine, naphazoline, clonidine, dobutamine, salbutamol….etc

  • Indirect; Release of NE from presynaptic stores at adrenergic nerve terminals

  • e.g. amphetamine

  • Or Inhibit uptake its availability in synapse.

  • e.g. Cocaine & antidepressants

Dual; Direct and indirect stimulation of adrenergic receptors

e.g. ephedrine, pseudoephedrine


ADRENERGICS AGONISTS

Direct Sympathomimetics


ADRENERGIC STIMULANTS

DIRECT Acting Sympathomimetics

ADRENALINE

Naturally released from adrenal medulla  2ndry to stress, hunger, fear

Inactivated by intestinal enzymes, so given parentral & by inhalation

Acts on all ADR; b =/> a .

Pharmacological actions see physiological actions of the SNS

Heart  inotropic, chronotropic, dromotropic & lusiotropic (excitability)(b1)

BP  systolic (b1)/ diastolic   low dose (b2)&  high dose (a1)

Vascular SMC; constrict skin + peripheral (a1) / dilate coronary +skeletal (b2)

Non vascular SMC;

Lung  bronchiodilatation(b2)

GIT  motility (b2)/ contract sphincter (a1)

Bladder   detrusor m. (b2)/ contract trigone & sphincter (a1)

Pregnant uterus  tocolytic(b2)

Eye  mydriasis(a1) /  no effect on accommodation or intraocular P

Metabolism insulin (a2), glucagon (b2), liverglycogenolysis + sk. m. glycolysis(b2) /   adipose lipolysis(b3 /b2)

CNS little, headache, tremors & restlessness


ADRENALINE

Indications

Used locally; as haemostatic (in epistaxsis) & as decongestant (a1) !!!

with local anesthetics  its absorption  toxicity & prolong action +  bleeding from incision

  • Used systemically for treatment of

  • Allergic reactions  drug of choice in anaphylactic shock as it is the physiological antagonist of histamine

  • Also in urticaria, angioneurotic edema & other hypersensitivity reactions due to   BP & cause vasoconstricton

  • In status asthmatics  given parentally  bronchodilatation(2) +  mucosal edema (a1)

    • N.B. Selective b2 are better in asthma by inhalation

  • In cardiac arrest  direct but now through central line

    • N.B. Selective b1 are better


ADRENALINE

ADRs

Tachycardia, palpitation, arrhythmias, angina pains

Headache, weakness, tremors anxiety and restlessness.

Hypertension  cerebral hemorrhage and pulmonary edema.

Coldness of extremities  tissue necrosis and gangrene if extravasation

Nasal stuffiness; rebound congestion if used as decongestion

Contraindications

  • CHD, hypertension, peripheral arterial disease.

  • Hyperthyroidism.

  • Closed-angle glaucoma  may IOP


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

NOREPINEPHRINE = NORADRENALINE

It is naturally released from postganglionic adrenergic fibres

Not used much therapeutically  severe vasoconstriction

Acts on a > b1

Only administered IV - Not IM or Subcutaneous necrosis

It  BP [ systolic & diastolic]  reflex bradycardia(vagal stimulation)

 CO not much changed

Indications

Used systemically; hypotensive states (inspinal anesthesia, in septic shock, if fluid replacement and inotropics fail) !!!

Used topically; as a local haemostatic

with local anesthetic !?


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

ISOPRENALINE

It is synthetic ; show no presynaptic uptake nor

breakdown by MOA  longer action.Acts on b >> a

10 times > broncho-dilatation Was used by inhalation in acute asthma

Used in cardiac arrest but contraindicated in hyperthyroidism & congestive heart failure [CHD]

DOPAMINE

Heart b1  force

Kidney D1 vasodilatation

+ diuresis

It is a natural CNS transmitter.

Released from postganglionic

adrenergic fibres (> renal vessels)

Releases NE from postganglionic adrenergic fibres

Acts on D1 > b1 > a1

Vessels a1


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

DOPAMINE

On heart 

Inotropic, no chronotropic effect

On BP  According to dose;

first  D1

then  due to b1

followed by a1 effect

Given parentrally by infusion

Indications

It is the drug of choice in treatment of SHOCK septic, hypovolaemic (after fluid replacement), cardiogenic

It  BP & CO (b1), without causing renal impairment (D1)

Can be given in acute heart failure (HF) but better dobutamine


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

DOBUTAMINE

It is synthetic. Given IV.

Acts on b1 > b2 > a1

On heart  Inotropic with little chronotropic effect

On BP  No or little  in therapeutic dose

(b1 & b2 counterbalance + no a1 )

Indications

Given parentrally by infusion for short term management of cardiac decompensationafter cardiac surgery, in acute heart failure [AHF].

It is preferred because

it does not  oxygen demand


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

PHENYLPHERINE

It is synthetic, noncatecholamine.

Given orally & has prolonged duration of action.

Acts as selectivea1

  • MIDODRINE

Peaks in 20 min.

t½ 30 min.

On heart  reflex bradycardia

On BP   due to vasoconstriction (a1 )

Indications

In Hypotension

Systemically;Pressor agent in hypotensive states. Infusion

Terminate atrial tachycardia(reflex bradycardia)

Nasal decongestant. Oral

Topically; Local Haemostatic, with Local anesthesia.

Decongestant (nasal & ocular)

Mydriatic(no cycloplegia)


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

Nasal & Ocular Decongestants

PHENYLETHYLAMINES

IMIDAZOLINE

Phenylephrine

Methoxamine

Naphazoline

Oxymetazoline HCI (Afrin)

Xylometazoline HCI (Otrivine)

Pseudoephedrine

N.B.Brimonidine is an imidazoline a2 agonist used in glucoma

Used for treatment of nasal stuffiness

But can cause Rebound nasal stuffiness

It is synthetic, imidazoline

Given orally or as patch.

Acts selectively on presynaptica2 & on Imidazoline Receptors

 BP  by action on (a2 ) at nucleus tractussolitarius to  sympathetic outflow to heart & vessels. Antihypertensive agent

CLONIDINE


ADRENERGIC STIMULANTS

Direct Acting Sympathomimetics

SALBUTAMOL

It is synthetic. Given orally, by inhalation or parentral.

Acts selectively on b2  on bronchi. Hardly effect on heart (b1)

Bronchodilater asthma & chronic obstructive airway disease (COPD)

N.B.Because t1/2 is 4 hrs longer acting preparations exist ; Salmeterol & Formoterol

Other selective b2 agonists :

Terbutaline; Bronchodilator & Tocolytic

Ritodrine; Tocolytic postpone premature labour

(labour that begins before the 37th week of gestation).


ADRENERGICS STIMULANTS [AGONISTS]

Indirect Sympathomimetics


ADRENERGIC STIMULANTS

INDIRECT Acting Sympathomimetics

AMPHETAMINE

It acts indirectly;

Releasing NE from adrenergic nerve endings > Blocking of its reuptake

Because it depletes vesicles from stored NE tachyphylaxsis

Absorbed orally, not destroyed by MAO, excreted mostly unchanged (by acidification of urine)

  • Acts on a& b similar to epinephrine but has CNS stimulant effects;

  • mental alertness, wakefulness, concentration & self-confidence / followed by depression & fatigue on continued use

  •  euphoria  causes its abuse…..

 Weight   appetite

 increase energy expenditure

No more used therapeutically  induces psychic & physical dependence and psychosis + the CVS side effects


ADRENERGICS STIMULANTS [AGONISTS]

Dual Sympathomimetics


ADRENERGIC STIMULANTS

DUAL Acting Sympathomimetics

EPHEDRINE

Plant alkaloid, synthetic, mixed sympathomimetic;

Prolonged direct action on receptors  receptor down regulation

Release NE from adrenergic nerve endings depletes stores

 tachyphylaxsis

Absorbed orally, not destroyed by MAO or COMT  prolonged action

Acts on a& b

+ > facilitation of neuromuscular transmission & retention of urine

+ has CNS stimulant effects (less than amphetamine)

No more therapeutically used  but is abused by athletes and prohibited during games.

Abuse in Athletes

Pseudoephedrine, dual acting < CNS & pressor effects compared to ephedrine. Used as nasal & ocular decongestant & in flue remedies.


  • Agents specifically indicated for hypotension

  • Midodrine, Phenylephrine, Norepinephrine, Phenylpropanolamine

  • Agents specifically indicated for cardiogenicshockAHF

  • Dobutamine, Dopamine, Epinephrine

  • Agents specifically indicated for shock

  • Dopamine,Norepinephrine

    • Agents specifically indicated for cardiac arrest Dobutamine,Epinephrine,Norepinephrine

  • Agents specifically indicated for bronchial asthma

  • Salbutamol, Salmeterol, Formoterol, Terbutaline, Isoprenaline

  • Agents specifically indicated for premature labour

  • Ritodrine,Terbutaline

  • Agents specifically indicated for nasal decongestion

  • Pseudoephedrine, Naphazoline, Oxymetazoline, Phenylephrine, Xylometazoline

  • Agents specifically abused in sports Ephedrine, Amphetamine


GOOD LUCK


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